From 10 to 12 tops and bottoms of 12-gallon Pyrex carboys (the bottoms are inverted). At the University of California Radiation Laboratory, at one time, centers were cut from such carboys for use in "cloud-chamber" experiments. Played on the edges with small soft mallets, also on the flat tops. The bowls give a bell-like tone, and each has at least one inharmonic overtone. When one of them breaks it is virtually impossible to find an exact duplicate.